Recent developments in the aerospace, automotive and marine industries have led to new manufacturing techniques and a continuing search for new materials that are characterized by high specific strength and modulus as well as high performance at elevated temperatures. Aluminum-based metal matrix composite materials reinforced by ceramic particulates, particularly titanium carbide, are considered to be promising materials which are characterized by high performance at elevated temperatures. The ceramic particulates are stable and non-dissolvable at temperatures up to the melting point of the aluminum matrix.
The mechanical properties of the aforementioned aluminum matrix composite materials are determined based on the average particle size of the particulates and their shape. The nano-metric spherical particles are recommended for obtaining superior properties at elevated temperatures. In general, the reinforced composites may be made by two different techniques, namely ex-situ and in-situ. In the ex-situ technique, the pre-manufactured ceramic particulates are added to the liquid metal by various fabrication methods such as squeeze casting, pressure infiltration and stirring. However, there is a major challenge with ex-situ manufacturing techniques. The problem relates to the non-wetting nature of ceramics by liquid aluminum.
In in-situ techniques, the surrounding particles are formed throughout the metal matrix by a chemical reaction. The ceramic phase is free of contaminants and a strong bond is formed between the ceramic and the metal phases. The difficulty with in-situ techniques are that the distribution homogeneity and the average particle size of ceramics are difficult to control. However, in in-situ synthesizing titanium as a transition element enters into an exothermic reaction with carbon producing TiC particulates having high coherency and strong interface with the metal as for example aluminum.
U.S. Pat. No. 5,041,263 of Sigworth relates to third element additions to aluminum-titanium master alloys. As disclosed therein, an improved aluminum-titanium master alloy containing carbon in a small but effective content and not more than about 0.1% are provided. After melting, the master alloy is superheated to about 1200°-1250° C. to put the carbon into solution, than the alloy is caste in a workable form. The master alloy in final form is substantially free of carbides greater than about 5 microns in diameter. The alloy is used to refine aluminum products that may be rolled into thin sheets, foil or fine wire and the like.
A more recent U.S. Pat. No. 5,698,049 of Bowden discloses a method for producing aluminum matrix composites containing refractory aluminide whiskers or particulates which are formed in-situ. Aluminum and refractory metal materials are blended in powder form and then heated to a temperature above the melting point of aluminum. A solid/liquid reaction between the molten aluminum and solid refractory metal provides a desired volume fraction of refractory aluminide reinforcement phase (in situ whiskers or particulates). Upon cooling the molten unreacted portion of aluminum solidifies around the in situ reinforcements to create the improved composite materials. As further disclosed the process involves blending together effective amounts of aluminum powder and a refractory metal powder to represent a desired volume fraction of reinforcement phase. This reinforcement phase is formed when a powder pack is placed in a niobium or other suitable can and heated under vacuum to a temperature above the melting temperature of the aluminum. This produces a chemical reaction between the molten aluminum and solid refractory metal powder that results in an in-situ formation of a refractory metal aluminide reinforcement phase. After the reaction is complete and upon cooling to room temperature, the residual unreacted aluminum solidifies and envelopes the reinforcements. The solid composite material is thereafter removed from the can.
A U.S. Patent Appl. Pub. No. 2003/0145685 is entitled “Process for Producing Titanium Carbide, Titanium Nitride, and Tungsten Carbide Hardened Materials.” As disclosed, precursor materials are heated to a temperature sufficient to form TiC, TiN or WC but at which the metal phase may softened but does not become molten (liquid). In this way the TiC, TiN or WC are formed in-situ without melting the metal phase. As stated in the aforementioned patent publication, “introducing a ceramic phase into a metal matrix provides characteristic features of each of the resultant products.” The ceramic increases hardness and wear resistance but is often brittle, which the metal or metal alloy contributes toughness and durability. However, “wetting” of the ceramic component by the metal to obtain cohesive bonding between the metal or metal alloy and the ceramic component is a major challenge to the preparation of such materials.
Notwithstanding the above, it is presently believed that there is a need and a potential commercial market for a process in accordance with the present invention. There should be a need because the present process provides in-situ formation of titanium carbide in an aluminum matrix composite. Further, such materials produced thereby have improved hardness and wear resistance as well as toughness and durability. In the present process, the ceramic and metals are formed with a cohesive bonding between the metal or metal alloy.